The use of three-dimensional images or shapes is becoming increasingly important, especially for applications such as showing objects on the Internet, virtual reality, the film industry and so on.
Three-dimensional shape descriptions are usually acquired with two or more cameras or using laser systems. Existing systems may have a high cost, may require a time-consuming calibration procedure and be difficult to transport, while in some cases the scene must be static, the working memory volume for the scene is determined or insufficient information concerning the topology of the shape is obtained.
An example of related research is an article by A. Blake et al., xe2x80x9cTrinocular active range-sensingxe2x80x9d, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 15, No. 5, pp. 477-483, 1993. According to this method, two series of parallel lines are projected sequentially. The lines in the image can be identified by ensuring that the projected lines and epipolar lines intersect laterally. The lines may not therefore be too close together.
Another example is an article by Vuori and Smith, xe2x80x9cThree dimensional imaging system with structured lighting and practical constraintsxe2x80x9d, Journal of Electronic Imaging 6(1), pp. 140-144, 1997. According to this method a single pattern is projected but, limitations are imposed on the dimensions of the scene for recording and on the relative distances between the pattern elements. This makes it possible to predict in which part of the image plane each individual pattern element is projected.
In addition, known systems and methods always start from absolute measurements and dimensions, which is not always required, particularly not when the application is aimed at showing and not at measuring the objects.
The present invention provides a method for acquiring a three-dimensional shape or image of a scene, wherein a predetermined pattern is projected onto the scene and the shape is acquired on the basis of the relative deformations of the pattern as detected in one or more images.
The invention further provides a system for acquiring a three-dimensional shape or image of a scene, including:
at least one pattern generator for projecting a pattern on the scene;
at least one camera for making an image or images of the scene;
computing means for determining the shape of the scene.
The required hardware is simple and the system according to the present invention is therefore not very expensive.
According to the present invention it is no longer required to individually identify components of the projected pattern, such as lines or dots, either via a code in the pattern itself or via limitations imposed by the scene and/or the arrangement or a priori knowledge in respect thereof. In the method according to the present invention the shape can be acquired via the relative positions of the components in the pattern, for instance by determining the relative sequence of pattern lines.
According to the present invention a single image will suffice to acquire a three-dimensional image or a three-dimensional shape description and an acquisition time is required which is no longer than that for making a single image.
Because the recording time of a single image can remain limited and since reconstructions can be performed for a quick succession of different images, moving objects and their three-dimensional movements and changes of shape can be reconstructed.
According to the present invention the calibration procedure can be kept simple and few limitations need be imposed on the relative position of the pattern generator(s) and camera(s).
According to the present invention the projected pattern can be kept very simple and strongly interlinked, such as for instance a grid of lines. Owing to the simplicity, the resolution of the pattern and thereby of the three-dimensional reconstruction can be kept high. Due to the strong interlinking of the pattern, it becomes possible to determine the correct surface topology explicitly as a component of the output.
According to the present invention the absolute position of components of the pattern within the entirety of the pattern is of secondary importance. Three-dimensional shape descriptions can be generated without such information, except for a scale factor, by assuming a (pseudo-)orthographic model for the geometry of pattern projection and image formation. Perspective effects in this geometry are preferably kept limited.
According to the present invention both the three-dimensional shape and the surface texture of scenes can be determined. It is herein possible to eliminate problems of alignment of shape and texture since shape and texture are determined using the same camera(s). The final output, which can be a three-dimensional shape description with or without texture, can of course be made in any desired format, including formats which are for instance suitable for graphic work-stations or Internet.
According to a preferred embodiment the surface texture can moreover be acquired from the same image that is used to determine the three-dimensional shape. A similar method can also be extended to cases where a pattern is employed with absolute definition of the components. It will be apparent that the procedure for acquiring coloured or multi-spectral surface texture, i.e., built up of different spectral base images, does not differ essentially from the procedures for one base image.
According to a preferred embodiment the projected pattern is regular and composed of similar basic shapes, such as rectangles or squares, formed by the composition of two mutually perpendicular series of parallel equidistant lines.
According to a preferred embodiment calibration takes place by showing the system two planes between which the angle is known, for instance a right angle. The parameters required for the shape definition can be determined herefrom, such as the angle of reflection of the projected rays relative to the image plane and, if necessary, the height/width ratio of the pixels.